The present invention relates generally to implantable, radially expandable medical prostheses which are frequently referred to as stent-grafts. In particular, the present invention is a self-expanding stent-graft having a bioabsorbable structural component and a permanent graft component.
Self-expanding stents and methods for fabricating a stent are known and are, for example, shown in the U.S. Pat. Nos. 4,655,771; 4,954,126; 5,061,275; and in 5,645,559. Such devices are used within body vessels of humans for a variety of medical applications. Examples include intravascular stents for treating stenoses, stents for maintaining openings in the urinary, biliary, tracheobronchial, esophageal, renal tracts, and vena cava filters. A stent-graft is described in U.S. patent application Ser. No. 08/640,253, entitled xe2x80x9cCobalt-Chromium-Molybdenum Alloy Stent and Stent Graftxe2x80x9d, filed Apr. 30, 1996.
A delivery device is used to deliver the stent-graft through vessels in the body to a treatment site. The flexible nature and reduced radius of the compressed stent-graft enables it to be delivered through relatively small and curved vessels.
All references cited herein, including the foregoing, are incorporated herein in their entireties for all purposes.
The present invention relates to a self-expanding stent-graft having a bioabsorbable structure such as a stent and a permanent graft bonded together with an adhesive. The implantable stent-graft may include a tubular, radially compressible, axially flexible and radially self-expandable structure made from bioabsorbable elongate filaments formed in a braid-like configuration and a graft made from materials such as polyethylene terephthalate (PET), expanded polytetrafluoroethylene (ePTFE), polycarbonate urethane (PCU) or polyurethane (PU). The graft may be adhered to a surface of the bioabsorbable structure or interwoven or braided into the bioabsorbable structure. The preferred graft of the stent-graft is made of braided, woven, or spray-cast PET, PCU, or PU fibers. The raft may also be made of film, sheet, or tube such as an ePTFE or PCU material. The graft is designed to remain permanently implanted in the body, however, small amounts of degradation may occur to the graft over time in the body environment.
The stent-graft generally assumes a substantially tubular form in an unloaded or expanded state when not subjected to external forces and is generally characterized by a longitudinal shortening upon radial expansion and a longitudinal lengthening upon radial contraction.
In a preferred embodiment, the bioabsorbable structure of the stent-graft assembly is a stent which substantially consists of a plurality of elongate polylactide bioabsorbable polymer filaments, helically wound and interwoven in a braided configuration to form a tube. The filaments may also be made of poly(alpha-hydroxy acid) such as poly-L-lactide (PLLA), poly-D-lactide (PDLA), polyglycolide (PGA), polydioxanone, polycaprolactone, polygluconate, polylactic acid-polyethylene oxide copolymers, modified cellulose, collagen, poly(hydroxybutyrate), polyanhydride, polyphosphoester, poly(amino acids), or related copolymer materials.
Each bioabsorbable material has a characteristic degradation rate in the body. For example, PGA and polydioxanone are relatively fast-bioabsorbing materials (weeks to months) and PLA and polycaprolactone are relatively slow-bioabsorbing materials (months to years).
PLA, PLLA, PDLA and PGA have a tensile strength of from about 276 millions of Pascals (MPa) to about 827 MPa (40 thousands of pounds per square inch (ksi) to about 120 ksi); a tensile strength of 552 MPa (80 ksi) is typical; and a preferred tensile strength of from about 414 MPa (60 ksi) to about 827 MPa (120 ksi). Polydioxanone, polycaprolactone, and polygluconate include tensile strengths of from about 103 MPa (15 ksi) to about 414 MPa (60 ksi); a tensile strength of 241 MPa (35 ksi) is typical; and a preferred tensile strength of from about 172 MPa (25 ksi) to about 310 MPa (45 ksi).
PLA, PLLA, PDLA and PGA have a tensile modulus of from about 2758 MPa to 13790 MPa (400,000 pounds per square inch (psi) to about 2,000,000 psi); a tensile modulus of 6206 MPa (900,000 psi) is typical; and a preferred tensile modulus of from about 4827 MPa (700,000 psi) to about 8274 MPa (1,200,000 psi). Polydioxanone, polycaprolactone, and polygluconate have a tensile modulus of from about 1379 MPa (200,000 psi) to about 4827 MPa (700,000 psi); a tensile modulus of 3103 MPa (450,000 psi) is typical; and a preferred tensile modulus of from about 2413 MPa (350,000 psi) to about 3792 MPa (550,000 psi).
The preferred design for the bioabsorbable structure of the stent-graft includes 10-36 filaments braided into a tubular mesh configuration. Alternative designs could be made using more than 36 bioabsorbable filament strands. Stent-grafts are envisioned having as many as 500 filaments and which are made with braiders having sufficient carrier capacity.
Stents for arterial indications typically require high radial strength to resist elastic recoil after PTA dilation of the muscular arterial wall tissue. The radial strength of a stent-graft can be increased by increasing the number of filament strands in the design. Also the amount of open space in the stent mesh of the stent-grafts can be reduced by using more filament strands. It may be desirable to utilize stents with less open space if there is concern that the endoprosthesis may become occluded due to the ingrowth of tumorous tissue from cancer. A stent with little open space could be used to purposely seal off branch vessels from the main artery. Larger diameter stent-grafts require more filament strands in the braid to build the structural network over the larger surface area. Large stent-grafts would be needed for the aorta and for the trachea and esophagus. Also, large stent-grafts could be used in the airway and esophagus to seal off fistulas or to prevent or limit tissue ingrowth into the stent.
The present invention advantageously provides an improved stent-graft and a methods for making and using such a stent-graft.
In sum, the invention relates to a stent-graft including a bioabsorbable structural support including a tubular body having open ends, a sidewall structure having openings therein, and an inside and an outside surface and a permanent graft having an inside and outside surface. One of the bioabsorbable structural support or the permanent graft cooperates with the other and provides a coextensive portion wherein at least a part of the coextensive portion has a length of the bioabsorbable structural support and a length of the permanent graft bonded or interbraided together. The coextensive portion may be part or all of the longitudinal length of the stent-graft. The stent-graft may be adjustable between a nominal state and a radially-reduced state. The tubular body may further include a plurality of bioabsorbable elements formed in a generally elongated shape which is generally radially compressible and self-expandable. The stent-graft may provide an initial radial force when implanted in a body lumen and the bioabsorbable structure portion bioabsorbs over time in-vivo with an eventual resulting decrease in radial force to the vessel wall, and the permanent graft portion substantially remains in the body lumen. The structural support and the permanent graft may be bonded by adhesive means and the adhesive means may be bioabsorbable. The adhesive means may occupy a proximal and a distal end portion but not a mid portion over the coextensive portion which the structural support and graft are coextensive one another. The bioabsorbable structural support may be made of at least one of poly (alpha-hydroxy acid), PGA, PLA, PLLA, PDLA, polycaprolactone, polydioxanone, polygluconate, polylactic acid-polyethylene oxide copolymers, modified cellulose, collagen, poly(hydroxybutyrate), polyanhydride, polyphosphoester, poly(amino acids), or combinations thereof and the graft may be made of at least one of PET, ePTFE, PCU, or PU. The elements may be substantially homogeneous in cross section and length. The graft may include a plurality of interwoven fibers, mono-filaments, multi-filaments, or yarns. The graft may be a film, sheet, or tube. The graft may form a composite wall with body tissue in the body lumen. The stent-graft may be permeated with body tissue and may provide structural support to a body lumen for less than about 3 years. The graft may be disposed on at least one of the inside and outside surface of the structural support. The graft and the filaments may be interbraided. The bioabsorbable structural support may be annealed.
The invention also relates to a stent-graft including a tubular, radially compressible and self-expandable braided and annealed structure having a first set of filaments each of which extends in a helix configuration along a center line of the stent and having a first common direction of winding. A second set of filaments each extend in a helix configuration along a center line of the stent and have a second common direction of winding. The second set of filaments cross the first set of filaments at an axially directed angle. Each filament includes bioabsorbable material and has a substantially solid and substantially uniform cross-section, a tensile strength of from about 276 MPa (40 ksi) to about 827 MPa (120 ksi), a tensile modulus of from about 2758 MPa (400,000 psi) to about 13790 MPa 2,000,000 psi), and an average diameter of from about 0.15 mm to about 0.6 mm. A permanent graft cooperates with at least a portion of the structure to form a stent-graft adapted to be disposed in a body lumen. The graft may conform with the structure. The first set and the second set may have the same number of filaments. Each of the first and second sets of filaments may include from about 5 filaments to about 18 filaments. The axially directed angle when in a free radially expanded state after being annealed but before being loaded on a delivery device may be between about 120 degrees and about 150 degrees.
The invention also relates to a method of making a stent-graft including braiding bioabsorbable filaments to form a tubular braid, the braid having a braid angle; disposing the braid on a mandrel; annealing the braid at a temperature between about the bioabsorbable filament glass transition temperature and about the melting point for a predetermined time to form an annealed stent; removing the stent from the mandrel, the stent having a filament crossing angle; providing a permanent graft; and adhering at least a portion of the graft to the annealed stent to form an assembly. The permanent graft may further comprise a braid angle and the method may further include prior to the step of adhering matching the braid angle of the permanent graft to about the stent filament crossing angle. The method may further include prior to the step of adhering, applying at least one of a thermoplastic adhesive, curable adhesive, and bioabsorbable polymer glue to the surface of the stent. The method may further include prior to the step of adhering, applying radial compression or axial elongation to the assembly to apply pressure over at least a portion of the stent and graft. The braid may be annealed at a temperature of from about 60xc2x0 C. to about 180xc2x0 C. for a period of time of from about 5 minutes to about 120 minutes or annealed at a temperature of from about 130xc2x0 C. to about 150xc2x0 C. for a period of time of from about 10 minutes to about 20 minutes.
The invention also relates to a method of making a stent-graft including braiding bioabsorbable elements to form a bioabsorbable tubular braid, the braid having a braid angle; providing a permanent graft film, sheet, or tube; disposing one of the permanent graft film, sheet, or tube or the bioabsorbable tubular braid on a mandrel; disposing the other of the permanent graft film, sheet, or tube or the bioabsorbable tubular braid over at least a portion of the other; adhering the permanent graft film, sheet, or tube to the braid to form a braid-graft; annealing the braid-graft at a temperature between about the bioabsorbable elements glass transition temperature and about the melting point for a predetermined time to form the stent-graft; and removing the stent-graft from the mandrel.
The graft film, sheet, or tube may include at least one of ePTFE and PCU and the bioabsorbable filament may include PLLA.
The invention also relates to a method of using a stent-graft including providing a tubular, radially self-expandable and radially compressible, axially flexible, braided and annealed structure comprising elongate bioabsorbable filaments. The filaments have a tensile strength of from about 276 MPa (40 ksi) to about 827 MPa (120 ksi), and a tensile modulus of from about 2758 MPa (400,000 psi) to about 13790 MPa (2,000,000 psi). Each filament has an average diameter of from about 0.15 mm to about 0.6 mm; providing adhesive means; and providing a permanent graft disposed and adhered with the adhesive means to at least a portion of the structure and forming a stent-graft assembly; deploying the stent-graft assembly into a body lumen at a treatment site; and allowing the stent-graft assembly to self-expand or expanding the stent-graft assembly in the body lumen. The bioabsorbable filaments may include PLLA, PDLA, PGA, or combinations thereof and the graft may include PET, ePTFE, PCU, or PU or combinations thereof.
The invention also relates to a method of using a stent-graft to regenerate a defective body vessel including disposing a stent-graft into a body vessel having a vessel wall with a defect in the vessel wall, and natural tissue generation ability. The stent-graft includes a bioabsorbable structure portion and a permanent graft portion and has an outside surface. The bioabsorbable structure portion provides temporary force to the body vessel and the permanent graft portion provides a permanent synthetic wall at the area of the defect in the body vessel and is receptive to growth of the natural tissue therein and thereabout; placing the stent-graft in the vicinity of the defect such that at least a portion of the stent-graft spans the defect in the vessel wall; providing contact between the outside surface of the stent-graft and the vessel wall whereby the stent-graft provides an initial radial force to the vessel wall; and allowing or promoting healing at or around the stent-graft, the bioabsorbable structure portion adapted to bioabsorb over time in-vivo with an eventual resulting decrease in radial force to the vessel wall, and the permanent graft portion adapted to substantially remain in the body lumen. The body vessel may be an artery. The permanent graft portion may be replaced over time by a composite wall including natural tissue and the permanent graft portion. The defect may be at least one of an aneurysm, fistula, occlusive disease, or recurrent occlusive disease. The defect may be substantially excluded from the body vessel by one of the stent-graft or the composite vessel wall.
Bioabsorbable resins such as PLLA, PDLA, and PGA are available from PURAC America, Inc. of Lincolnshire, Ill. Partially oriented yarns and flat yarns are commercially available from Wellman Inc. of Charlotte, N.C. The partially oriented yarns can be textured by Milliken, Inc. of Spartenburg, S.C. Silicone adhesive is commercially available from Applied Silicone of Ventura, Calif. The remaining materials discussed in the application are commercially available.